1. Field of the Invention
This invention relates to temperature controlling devices for air conditioning systems and more specifically for temperature controlling devices that detect a loss of refrigerant or loss of cooling capability for an air conditioning device.
2. Description of the Prior Art
Air conditioning systems have traditionally included a thermostat switch that provides a hysterisis or cycling of the air conditioning unit when cooling an area. Specifically, the thermostat turns on the air conditioner until the air conditioner has cooled the area and a specific temperature has been achieved. At this point, when the temperature of the area is below a certain set value by the thermostat, the thermostat will turn off the air conditioning unit. The air conditioning unit will remain off until the cooled area warms up enough so that the temperature of the area reaches a second point which is detected by the thermostat. Upon reaching this second point, the thermostat turns on the air conditioning unit again to provide additional cooling. This "on/off" cycling is continued to provide cooling within a small temperature range.
If the air conditioner loses refrigerant or loses cooling capability, the air conditioning unit will continue to run even though adequate cooling is not occurring. If this condition is allowed to continue, energy is wasted. Furthermore, where a loss of refrigerant has occurred, the compressor of the air conditioner may be damaged.
Traditional means to detect a loss of charge or lack of cooling capability include temperature sensors and pressure sensors. Temperature sensors have been used to detect excessively high temperatures indicating a failure of the air conditioning cooling capability. Temperature sensors have also been used to detect levels of the refrigerant in a refrigerant reservoir. Pressure sensors have been used at points in the compressor line to detect the loss of charge by detecting a loss of pressure.
However, the use of temperature sensors or pressure sensors by themselves will only detect failures at absolute temperature or pressure values. Degradation of cooling capability will not be detected by these sensors until the specific value is reached.
It is an object of this invention to provide for the detection of loss of refrigerant charge or loss of cooling capability by detecting a decrease in the rate of cooling of the air conditioner device.